Devices have been developed for collecting and collimating light from a small light source, such as an incandescent, LED, or the like. Often such devices use a reflective parabolic structure which are designed to collimate the light from a point source placed at the focus of the reflector due to the divergent nature of the light source. The light striking the structure is redirected parallel to the axis of the parabola, exits out the open end of the reflector, and propagates as a narrow, well-confined beam. In practice the source is not a point, but has some spatial extent and, as a result, the actual divergence of this reflected beam is determined by the size of the reflector and by the finite, i.e., non-zero, size of the source. Also, the quality of the beam of light in the far field is poor, forming a ring structure caused by the base of the reflector being blocked by the light source. An additional drawback of reflective parabolic structure designs is that the light from the source which does not strike the reflector propagates out the open end of the reflector un-collimated. To correct these issues, some designs, such as those often used in flashlights, incorporate a lens element at the open end of the reflector. The lens captures both the direct light from the source and the light from the reflector. If the lens is made to collimate the direct light then it will cause the reflected light to be highly divergent. Since true collimation of all the light from such an arrangement cannot be achieved, such designs compromise between the divergence of the light and the uniformity of the resulting beam.
Catadioptric designs incorporating both reflection and refraction in a single optical component have been proposed which often operate by total-internal-reflection (TIR) using parabolic or conical wall structures. For example, Bittner in U.S. Pat. No. 2,215,900 describes a multi-surfaced rotationally-symmetric optical element with aspheric surfaces and a recess or cavity on one side for positioning the light source, such as a small flashlight bulb. Marshall et al., U.S. Pat. No. 6,547,423 describes a rotationally symmetrical, bowl shaped collector lens formed from a single material with an indentation in the bottom a light source. In U.S. Pat. No. 6,819,505, Cassarly et al. has a similar design as a collector of the light from the source, but it does not collimate the light. Instead, it transmits the light from a collector portion through a transition section to a projector lens. The collector portion substantially focuses the light within the transition section to produce a substantially circular light distribution. The light is then refracted by the projector lens section to produce a highly collimated beam.
These designs work to produce a fairly well collimated beam of light from a small light source. This limits their use for general lighting applications without the use of some diffuser or other light control device. Although diffusers have been used to smooth light over an area in general lighting applications, such as diffusing panel for fluorescent light, or diffusing surfaces in incandescent lighting fixtures, they have not been adapted to work with small divergent light sources, such as LEDs. However, passing light such a small divergent light source collimated as described in the above cited patents through a typical general lighting diffuser will provide poor results since the collimation needed to efficient collect light from the source will cause non-uniform light patterns having undesirable bright spot(s). It is thus desirable to use collimated light from low power light sources, such as LEDs, in general lighting applications by combining with a diffuser designed to provide uniform light over a desired angle that can also be used in tailored lighting applications, such as in architectural and industrial lighting.